In accordance with an increased interest in safety of cars, requests for not only a low fuel consumption but also steering stability have been increased. In order to meet the requests, tires highly satisfying low heat build-up achieved by reducing rolling resistance, steering stability on wet road surfaces and dry road surfaces, and abrasion resistance in tire performances have been required. Also, in order to achieve such requests as described above, reinforcing fillers and rubber components are tried to be improved.
Carbon black has so far been used as a filler for reinforcing rubbers. This is attributable to that carbon black can provide a rubber composition with high abrasion resistance. However, it is difficult to obtain by using singly carbon black a rubber composition in which a wet grip performance, abrasion resistance and a low fuel consumption are balanced at a high level, and silica is compounded instead of carbon black as an improving method therefor. However, it has been found that when silica is used as a filler, a blending amount of carbon black is relatively reduced, so that the rubber composition is inevitably reduced in fracture strength and abrasion resistance. Also, involved therein is the problem that silica has inferior dispersibility in rubber and that a rubber composition is increased in a Mooney viscosity in kneading and inferior in processability such as extrusion.
Rubber compositions for tire tread containing rubber components and inorganic compound powders in addition to carbon black and silica as fillers for the purpose of obtaining rubber compositions which are excellent in a low fuel consumption and a wet grip performance without lowering abrasion resistance are proposed in patent documents 1 to 3.
However, in the rubber compositions described in the patent documents 1 to 3, the inorganic compound powders have to be compounded in a relatively large amount in order to obtain a satisfactory effect of improving a wet grip performance and a fuel consumption. In the case, the abrasion resistance tends to be readily reduced, and therefore a rubber composition for tire which is further excellent in a balance between a wet grip performance, abrasion resistance and a low fuel consumption is not obtained.
Also, a rubber composition for tire tread which is improved in a wet grip performance and abrasion resistance by using carbon black specified in a characteristic calculated from two-dimensional projection image analysis of aggregates and properties such as DBP, N2SA in addition to a diene base rubber component and silica is proposed in patent document 4. However, it does not sufficiently satisfy as well a low fuel consumption in addition to a wet grip performance and abrasion resistance.